A lamp of such a type includes a first lamp unit configured to mainly form a low beam and a second lamp unit configured to mainly form a high beam, in order to form two types of light distributions, e.g., a low beam light distribution and a high beam light distribution. With a recent demand for a compact size, a lamp that includes first and second light sources that are arranged above and below a plate-shape support member to share a projection lens so as to form a plurality of light distributions with a single lamp unit (see, e.g., Japanese Patent Laid-Open Publication No. 2005-108554).